Spray drying carbon black



United States Patent 3,433,660 SPRAY DRYING CARBON BLACK Merrill E. Jordan, Walpole, and John F. Hardy, Andover,

Mass., assignors to Cabot 'Corporation, Boston, Mass.,

a corporation of Delaware No Drawing. Filed June 24, 1965, Ser. No. 466,823 US. Cl. 106-307 2 Claims Int. Cl. C09c 1/58 ABSTRACT OF THE DISCLOSURE A process for converting a special nitric acid oxidized, high color carbon black to an agglomerated state having a bulk density even higher than normal pellets but composed of very fine aggregates much smaller than normal pellets, which fine aggregates are readily dispersible in liquid vehicles on conventional equipment such as three roll mills which are normally used for producing inks and enamels. The key step in this process is the spray drying of a liquid slurry of such a black made with an anionic dispersing agent in appropriate concentrations.

This invention relates to carbon black. More particularly the invention disclosed herein relates to a process for producing a superior high color carbon black which imparts especially desirable properties to enamel systems and the like. Also included within the scope of the present invention are the products resulting from the novel process hereinafter disclosed.

The basic requirements for any color black are high jetness, easy dispersion in appropriate vehicles and good viscosity stability in resultant dispersions. In turn, the properties of the black which are responsible for these characteristics, and accordingly reflect the coloring efiiciency of a black are its nigrometer scale, particle size, volatile content, and to some extent, the physical nature of the volatile matter thereon.

The nigrometer scale of a carbon black is a measure of the masstone or the intenseness of jetness or blackness and is closely related to the particle size thereof. In general, the lower the particle size of a carbon black, the lower its scale and the more intense is the blackness thereof. According to recognized standards of the industry high color blacks are those with scales below 70, while the scales of medium color blacks have scales from about 70 to 78 and regular color blacks have scales from about 80 to 90. Another property of importance in color blacks is volatile content which often effects tone and color properties and usually determines flow properties of lacquers and enamels in which carbon black is compounded. The volatile content of a carbon black is an indication of the amount of chemisorbed oxygen and/or other gases on the surface thereof and is determined by measuring the loss of weight on calcining a dried carbon black sample in a covered platinum crucible for seven minutes at about 972 C. The regular color blacks generally have volatile contents of no greater than about by weight, whereas the volatile content is generally in the range from 5 to 10% by weight for medium color blacks and runs as high as 18% or more for high color blacks.

In commonly owned application Ser. No. 159,786, filed Dec. 15, 1961, by Jordan et al. now issued as US. Patent 3,226,244, the invention of a particularly advantageous high color black was disclosed for the first time. The process disclosed in the aforementioned application, however, although highly advantageous when pelleted forms of carbon black are to be produced, has been found less useful for the production of fluify blacks which are normally desirable for easy dispersion by less intensive dispersing apparatus than is used for dispersing pelleted blacks. The

reason for pelleting blacks is to avoid the extreme dustiness and low bulk density inherent in the flutfy blacks.

Therefore, it is an object of the invention to provide a method for producing high color carbon blacks having excellent dispersibility.

It is another object of the invention to produce a black having a unique combination of high bulk density and easy dispersibility in enamel systems.

A further object of the invention is to provide a carbon black of high to moderate bulk density which is dispersible by apparatus normally used for dispersing fluffy blacks.

It is a further object of the invention to provide a process which is especially suitable for producing non-pelleted high color carbon blacks capable of imparting superior tone, color, gloss, and viscosity stability to the enamel systems in which they are utilized.

A further object of the invention is to provide high bulk-density carbon blacks of small and easily dispersible secondary agglomerates and a process for making the same.

Still other objects of the present invention will be drying the dispersion to form the' product of the invention.

Applicants have substantially met the above objects of the invention with a unique process wherein a dispersion of carbon black spray dried to form free-flowing secondary agglomerates having extraordinary dispersibilty and density.

In general the process of the invention comprises (1') preparing, with the aid of a dispersing agent, a dispersion of carbon black in a liquid such as water, and (2) spray drying the dispersion to form the product of the invention. The product formed is believed to be novel in that no other known carbon black has the combination of dis persibility and bulk density advantages provided by the process of this invention. Non-pelleted blacks having bulk densities of over 10 lbs./ft. may be formed by the process of the invention. The most advantageous products of the invention have bulk densities of from, about 25 to about 40 lbs./ft.

The following procedures typify preparation of some of the high color channel carbon blacks which are advantageously used as starting products for the process of the invention. These blacks are produced by reacting blacks having an average diameter, as determined by electron microscopy, of at least about 15 mil'licrons and a porosity below about 200 with molecular oxygen at elevated temperatures.

For the purposes of the present invention, the porosity of a black is the difference obtained by deducting from the nitrogen surface area of a black (determined by the method of Brunauer-Emmett-Teller) that surface area of the black obtained by calculating same from the observed average electron microscope particle diameter according to the following formula: Square meters per gram =60,000/ 1.82 (E.M. particle diameter in angstroms). The difference obtained is generally believed by those well skilled in the art to be primarily due to the presence of small openings or pores in the surface of the black. The resultant :blacks are intermediate products having a porosity of between about 220 and 400. The intermediate products are then reacted with an oxidizing agent such as nitric and/or a nitric oxide to increase the volatile content by about 40%. The following examples illustrate the production of carbon blacks which may be used as starting materials in the process of the instant invention.

Example 1 600 grams of Monarch 74, a channel black produced by Cabot Corporation and having a nitrogen surface area of 230 square meters per gram, an average electron microscope particle diameter of 17 millimicrons and a porosity of about 130, were air aftertreated by passing 20 cubic feet of air per hour thereover while the black was slowly rotated in a 6 inch diameter by 12 inch long cylinder maintained at 1000 F. for 6 hours. The so air afterminutes at a temperature of 70 F. The mixture was then heated in a drum type dryer turning at 3.3 revolutions per hour for 8 hours at a constant temperature of 190 F. The final pigment had a nigrometer scale of 72.4%, a percent volatile of 15.7 and a density of 25 lbs./ft.

treated black had the following Properties! The system in which these carbon blacks are slurried Scale 745 in the process of the present invention is conveniently an Apparent bulk density (lb jftfi) aqueous system although, where economical and conven- V l til nt t (percent) 10 ient, other liquid dispersion media may be used.

N surface area (M /gm.) 500 10 Among dispersing agents which are advantageous for Average electron microscope use in the process of the invention are anionic surfactants Particle diameter (millimicrons) porosity 284 such as a partially desulfonated sodium lignosulfonate Various concentrations of the above air aftertreated sold under the trade e rasperse CB by Marathorn black were further treated by slurrying same with aqueous Corporatlon and Q m P Potasslum Salts of alkylated nitric acid solutions of various concentrations for various 15 naphthalene Sulfohle aelds sold under the trade name lengths of time and at various temperatures. The so DaXad 11 y Grace and In View of this treated blacks were subsequently heated until dry and closure, various other dispersing agents may be selected the following data were obtained: by those skilled in the art for use in the process of the in- Blaek cone. HNOa cone. Reaction Temp. Drying Drying Percent No. in slurry in liquid time reaction time temp. Scale vol.

(percent) phase (min.) F.) (hours) F.)

(percent) 1 50 15 30 so 16 230 71.5 27.2 2 10 15 30 so 16 475 74.4 13.6 3 10 5o 30 so 16 230 74.3 19.0 4 10 15 30 so 24 230 73.8 15.7 5 1o 40 30 so 16 230 73.4 16.9 6 10 15 30 so 16 230 74.7 14.8 7 20 40 so 16 230 72.4 16.1

Example 2 30 vention. Conveniently 5 to 6%, based on the weight of 500 lbs. of a carbon black having a nitrogen surface carbon i of the aforesaid. dispersing agents may area of 380 square meters per gram and an average elecused In gerieral the quantity may.be decreased or tron microscope particle diameter of 16 millimicrons and created dependmg Pamculair clrcumstances of the a porosity of about 178 were air aftertreated by continslurimg procedure unhzed any gwen case ually passing air thereover while the black was slowly Since the next i p l slurry of the carbon black rotated in a cylinder maintained at a temperature of about be Spray drying 1t Wm p understood a Sufficlcm 1000" F. for about 4 hours. The so air aftertreated black hquld Shquld be used as a dlspersant Provide an adehad the following properties: quate carrier for the carbon black and facilitate the passage of the slurry through the apertures of the spray drymg Scale 70 apparatus. On the other hand, economics of a spray drying pp bulk density 20 process dictate that as little liquid be used as is practical Volatile Content (P 10 to achieve the desired results. This is of course, to conserve 2 Surface area B 550 energy required to evaporate the aforementioned liquid Average electron mleroseepe 15 carrier from the carbon black product. Particle diameter (millimlel'ohs) P W 334 In practice, it has been found that about 100 parts of A sample of a carbon black Prepared in the above a carbon black can be advantageously slurried in about 400 described manner was slurried with nitric acid in a 25 Parts of Water E form a slurry of abojlt by weleht r.p.m. pelletizer for 30 minutes at a temperature of 90 carbon black Yvlth aboui 6 Pe of a dlsperslhg agent llke R The concentration of the black in the Slum-y was 475% the aforementioned sodlum llgnosulfonate sold under the and the concentration of the HNO in the liquid phase trade name M f p re a hlgher carbon blackwas 11.8%. Thereafter, the black was heated at a constant tofwater who 15 e Somewhat more dlspel'slhg agent temperature of 275 F. for 9 hours in a drum dryer main- W111 ly reqlllred; ere a lower carbon black-totained at about 30 The pigment produced had a water who is used, somewhat less dispersing agent W111 nigrometer scale of 70.0, a percent volatile of 17.1% and usuanX be requll'ed- Furtherfhhre, the Parhcle Size may a density of 333 1 3 be varied somewhat by modifying the speed of the spray wheel and the dispersion concentration of the carbon Example 3 bl k,

A carbon black having a nitrogen surface area of Spray drying is conveniently accomplished by feeding about 180 M d an average 1 t microscope the carbon black slurry, conveniently at room temperature, diameter of about 20 millimicrons and a porosity of about into a spray drying apparatus as is known to the art. Con- 36 was air aftertreated by passing 25 cubic feet of air Venienfly, hot gases Will he Conducted into the Chamber per hour thereover while the bla k wa slowly rotated at temperatures about 550 F. and exhausted at about 230 in a 6 inch diameter by 12 inch long cylinder maintained F., although other temperatures may be used where ecoat 1200 F. for 8 hours. The so air aftertreated black had nomics or other conditions make them so desirable. Of the following properties: 35 course, in any event, the temperatures must be sufficiently Scale 73 2 lighkti) elyaporajte suflficient1 of the liquid in which the car- 7 on ac as een s urrie gggzg s is i (lbs/it's) When the process is carried out using the carbon black N surface area 480 of Example 3 above and the aforementioned process con- Agerage demon microsop'e 17 ditions, the product 1s a free-flowlng black powder having Particle diameter gig g i 299 a bulk denslty of from 30 to 35 lbs. per cublc foot. Thls high bulk density is typical of, and in most cases even Thereafter, a slurry was formed containing 25% by greater than, bulk densities of pelletized carbon blacks. Yet weight of the aftertreated black using 20% HNO by the instant product is comprised of secondary agglomerates weight in the aqueous liquid phase and agitated for 40 75 much smaller than those encountered in the pelletized blacks known to the art. Moreover, the size of these agglomerates contributes to the products being easily dispersible on apparatus providing relatively mild dispersing action. For example, 3-roll mills, 2-ro1l mills, dough mixers and the like.

The following screen analysis (U.S. Series) is typical of the product of the invention:

Percent Retained on 125 mesh 7.4 Passed 125 mesh; retained on 140 mesh 1.3 Passed 140 mesh; retained on 200 mesh 16.9 Passed 200 mesh; retained on 270 mesh 68.0 Passed 270 mesh; retained on 325 mesh 3.8 Passed 325 mesh 1.8

As observed from the preceding table the size of the secondary agglomerates is predominantly finer than 140 mesh.

To illustrate the facility with which the product of the invention may be dispersed, the material was compounded with (1) relatively fast air-drying styrenated alkyd resin and (2) a relatively slow-drying styrenated alkyd resin on a 3-roll mill. The resultant products were compared with analogous products prepared with two other carbon blacks, A and B, described below.

The fast-air drying styrenated alkyd resin systems were prepared by dispersing 20 parts of carbon black in 200 parts of a styrenated alkyd resin, sold under the trade name Cycopol 8101-1 by Koppers Company, on a 3-roll mill. Then 88 grams of the resulting mill paste were compounded with 160 grams of Cycopol 8101-1 and 40 grams of xylol to form the fast-drying systems.

The slow-drying alkyd resin systems were prepared by dispersing 20 parts of carbon black in 200 parts of an alkyd resin sold under the trade name Aroplaze 1085M-50 by U.S. Industrial Chemicals Company on a 3-roll mill. Then 88 grams of the resulting mill paste were compounded with 200 grams of Aroplaze 1085M-50, 15 grams of mineral spirits, 0.6 gram of a 6% cobalt drier, 1.2 grams of a 24% lead drier, and 0.4 gram of an antiskinning agent sold under the trade name Eskin No. 2.

Black A was a fluffy high color channel (HCC) black having an average diameter of about 120 A., and Black B was a sample of the raw material, i.e. the same kind of HCC black which had been dispersed and spray dried to give the instant product and the preparation of which is described in Example 2. Black B however, was micronized in an attempt to obtain the smallest possible particle size before the tests were run.

Evaluations of Black A, Black B and the instant product were made in respect to color (darkness) and color quality (blueness). The color properties of each of the resulting lacquers were determined on glass panel drawdowns of the black lacquers using apparatus sold under the trade designation Coloreye produced by Instrument Development Laboratories, Inc. of Attleboro, Mass. and described in detail in their Instruction Manual No. IOOOG for Model D Coloreye. The Coloreye measures light reflectance of a sample compared to a standard at three wave lengths, X, Y and Z, in the visible light spectrum. These wave lengths are red, green and blue wave lengths respectively. The lower reflectivity readings are considered the most desirable since lower reflectivity indicates greater absorption and darker color. The Blueness Factor is computed by the relationship X 100: Blueness Factor wherein X, Y and Z are the reflectivities at the aforesaid wave lengths. A lower Blueness Factor denotes a bluer" and therefore a more desirable tone to the blacks color characteristics.

Slow drying system Blueness factor X Y Instant product 125. 5 123 120.5 4.1 Black A 100. 0 100. 0 100. 0 1. 0 Black B 146. O 139. 0 131. 0 10. 8

Fast drying system Blueness factor X Y Z Instant product 81 80. 5 89. 5 10. 6 Black A 100 100 1. 0

Furthermore, in both systems use of the instant product contributed a considerable improvement in viscosity stability to the product:

Slow drying system Initial viscosity Viscosity after 16 hrs. at F.

Instant product 72 76 Bla k A 74 82 72 75 Fast drying system Initial viscosity Viscosity after 16 hrs. at 140 F.

Instant product 63 63 Black A 70 84 The viscosity measurements are given in terms of Kreb units known to the art.

From the foregoing, it is clear that the product of the invention is a superior carbon black to Black B when dispersed on such equipment as 3-roll mills and that the product is clearly superior to HCC blacks in blueness and viscosity stability, and also superior in color to other HCC blacks in some circumstances. Moreover, the tests clearly demonstrate the surprising improvement in color properties imparted to carbon black by the method of the invention.

It is of course to be understood that numerous changes can be made in the ingredients, proportions and conditions set forth above without departing from the spirit of the invention as defined in the appended claims.

What is claimed is:

1. A process for producing a nonpelletized free flowing carbon black in the form of easily dispersible secondary agglomerates of high bulk density which process comprises forming in the presence of an anionic dispersing agent, an atomizable aqueous slurry containing at least about 20% by weight of a high color carbon black said carbon black having been prepared by (1) treating a carbon black having an average electron 'microscope particle diameter of at least about 15 millimicrons and a porosity below about 200 with molecular oxygen at elevated temperatures to produce an intermediate product having a porosity between about 220 and about 400 and (2) reacting said intermediate product in a slurry with an oxidizing agent chosen from the group consisting of nitric acids and nitric oxides to increase the volatile content by at least 40%, and spray drying said atomizable aqueous slurry under conditions which yield easily dispersible secondary agglomerates of carbon black which are predominantly below 140 mesh in U.S. series screen size and which have a bulk density of at least 25 lbs./cu. ft.

2. The process of claim 1 wherein the anionic dispersing agent is used in amounts of about 5 to 6% by weight based on the weight of carbon black.

References Cited UNITED STATES PATENTS Tucker 106-307 Guertler et a1. 106309 Behn et a]. 106-309 Jordan et a1. 106307 8 OTHER REFERENCES Spray Drying Pigments, American Ink Maker. February 1959, pp. 30, 31, 57, 59.

5 TOBIAS E. LEVOW, Primary Examiner.

SAMUEL E. MOTT, Assistant Exam iner- US. Cl. X.R. 

